Centrifugal compressor

ABSTRACT

A centrifugal compressor includes a passage forming member being arranged in a rear side of an impeller fixed to a tip side of a rotor shaft, and forming a passage, together with a scroll member, and a casing member disposed adjacent to an opposite side of the passage forming member from the impeller along an axial direction. The passage forming member has a first protrusion, and the casing member has a second protrusion. The first protrusion and the second protrusion are fixed to each other by a bolt member inserted from an outside in a radial direction toward an inside in the radial direction.

TECHNICAL FIELD

This disclosure relates to a centrifugal compressor.

BACKGROUND

A centrifugal compressor is known as a rotating machine, which iscapable of compressing fluid by use of centrifugal force. Such acentrifugal compressor rotates an impeller attached to a rotor shaft togenerate compressed fluid. The rotor shaft is rotatably supported by abearing, and the impeller is fixed to at least one end side of the rotorshaft.

As for a rotor shaft having a cantilever structurer, an impeller isfixed to the rotor shaft in the tip side with respect to the positionsupported by a bearing, and the diameter of the impeller is larger thanthe diameter of the rotor shaft. Therefore, it is important to suppressthe shaft vibration from occurring during rotation, and to prevent theimpeller fixed to the rotor shaft from contacting with a peripheralmember. In an example, Patent Document 1 discloses the configurationadvantageous in suppressing shaft vibration, in which a nut for fixingan impeller to a rotor shaft is arranged inside the impeller so that thecenter of gravity of the rotor is shifted to a bearing.

CITATION LIST Patent Literature

Patent Document 1: JP2011-52580A

SUMMARY

A downsized rotor is advantageous in suppressing the shaft vibrationfrom occurring and in preventing the impeller from contacting with aperipheral component in the description above. Although, in PatentDocument 1 described above, a nut is arranged inside an impeller so asto provide a shorter rotor, resulting in contributing to the suppressionof the shaft vibration, there is room for further improvement.

At least one aspect of the present disclosure has been proposed in thelight of the above-described circumstances. The present disclosure is toprovide a centrifugal compressor capable of suppressing the rotorvibration from occurring in the rotor shaft during driving, andpreventing the impeller fixed to the rotor shaft from contacting with aperipheral component.

A centrifugal compressor according to one aspect of the presentdisclosure and capable of coping with the above includes: a rotor shaftrotatably supported by a bearing; an impeller fixed to the rotor shaftin a tip side with respect to the bearing; a passage forming memberbeing arranged in a rear side of the impeller, and forming a passagecommunicating with a scroll passage, together with a scroll memberforming the scroll passage outside the impeller in a radial direction;and a casing member disposed adjacent to an opposite side of the passageforming member from the impeller along an axial direction. In thecentrifugal compressor, the passage forming member has a firstprotrusion formed to protrude toward the casing member, the casingmember has a second protrusion formed to protrude toward the passageforming member, and the first protrusion and the second protrusion arefixed to each other by a bolt member inserted from an outside in theradial direction to an inside in the radial direction.

At least one aspect of the present disclosure enables suppressing thevibration from occurring in the rotor shaft during driving, and furtherpreventing the impeller fixed to the rotor shaft from contacting with aperipheral member.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating a schematic configuration of acentrifugal compressor according to one aspect of the presentdisclosure.

FIG. 2 is a cross-sectional configuration diagram of a vicinity of aturbo blower according to one aspect of the present disclosure.

FIG. 3 is a cross-sectional view at an A-A line shown in FIG. 2.

FIG. 4 is a cross-sectional view at a B-B line shown in FIG. 3.

FIG. 5 shows a modification of FIG. 3.

FIG. 6 shows another modification of FIG. 3.

FIG. 7 is a cross-sectional view at a D-D line shown in FIG. 6.

FIG. 8 shows another modification of FIG. 3.

FIG. 9 shows another modification of FIG. 4.

FIG. 10 is a cross-sectional configuration diagram of a vicinity of aturbo blower according to the reference art.

DETAILED DESCRIPTION

Some embodiments of the present invention will now be described belowwith reference to the drawings. However, the scope of the presentinvention is not limited to the embodiments described below. It isintended that sizes, materials, shapes, relative positions and the likeof components described in the embodiments below are merely examples,and are not for limitation of the scope of the present invention.

FIG. 1 is a perspective view illustrating a schematic configuration of acentrifugal compressor 1 according to one aspect of the presentdisclosure. The centrifugal compressor 1 is a geared compressor(integrally geared compressor) in which a speed-increasing gearmechanism 2 speeds up power and transmits the power to a rotor 4 so asto compress fluid. The speed-increasing gear mechanism 2 has a maindriving shaft 6 which accepts power from a power source (not shown), anda main driving gear 8 connected to the main driving shaft 6. The rotor 4includes a driven gear 10 engaged with the main driving gear 8, a rotorshaft 12 connected to the driven gear 10, and an impeller 14A and animpeller 14B respectively provided at the tips of the rotor shaft 12.

When power is input from a power source to the speed-increasing gearmechanism 2 via the main driving shaft 6, the main driving gear 8 isrotated together with the main driving shaft 6. The rotation rotates therotor 4 via the driven gear 10 engaged with the main driving gear 8.When the rotor 4 is rotated, the impellers 14A, 14B compress fluid byusing the centrifugal force generated by the rotation of the rotor shaft12.

It is noted that, in the description below, the extending direction of arotation axis C of the rotor shaft 12 is called an axial direction; thedirection of the circumference around the rotation axis C is called acircumferential direction; and the direction of the diameter of thecircumference is called a radial direction. Moreover, the side close tothe rotation axis C with respect to the radial direction is called aninside in the radial direction, and the side far from the rotation axisC with respect to the radial direction is called an outside in theradial direction.

The centrifugal compressor 1 has a gear casing 16 configured toaccommodate the speed-increasing gear mechanism 2, and a turbo blower18A and a turbo blower 18B respectively including the impellers 14A,14B. The turbo blowers 18A, 18B are arranged respectively on the bothsides in the axial direction with respect to the gear casing 16, so asto correspond to the impellers 14A, 14B.

The turbo blower 18A has an inlet passage 19 for taking in the fluid tobe compressed from an upstream passage, and an outlet passage 15 fordischarging the fluid after compression to the outside. The inletpassage 19 is communicated with an inlet pipe not shown and the outletpassage 15 is communicated with an outlet pipe not shown. As will bedescribed below with reference to FIG. 2 and FIG. 10, the turbo blower18A has, outside the impeller 14A in the radial direction, a dischargescroll 24 which forms the outlet passage 15 and which extends long inthe radial direction to the outside of the gear casing 16.

The turbo blower 18B has the same configuration as the configuration ofthe turbo blower 18A described above, except that the position andorientation to be arranged are different. In the following description,the configuration of the turbo blower 18A is mainly described. Unlessotherwise stated, the configuration of the turbo blower 18B is the same.

Reference Art

The internal configuration of the centrifugal compressor 1 is nextdescribed specifically. The reference art serving as a prior art isdescribed first. FIG. 10 is a cross-sectional configuration diagram ofthe vicinity of the turbo blower 18A according to the reference art.

The turbo blower 18A includes an impeller casing body 20, and a passageforming member 22, together with the impeller casing body 20, formingthe outer casing of the turbo blower 18A. The impeller 14A fixed to thetip of the rotor shaft 12 extending along the rotation axis C isaccommodated in an internal space S defined by the impeller casing body20 and the passage forming member 22. The impeller casing body 20 mainlysurrounds the impeller 14A from the tip side (from the outside in theaxial direction), and accommodates the discharge scroll 24. The passageforming member 22 is arranged in the rear side (inside in the axialdirection) of the impeller 14A, and forms, together with the impellercasing body 20, a communication passage R communicating the internalspace S and the discharge scroll 24.

The passage forming member 22 is fixed to the impeller casing body 20outside the gear casing 16 in the radial direction, by a first boltmember 23 inserted along the axial direction. The first bolt member 23is inserted into a first hole part 25 formed from the passage formingmember 22 over to the impeller casing body 20, to fix the passageforming member 22 and the impeller casing body 20 to each other.

At least one set of the first bolt member 23 and the first hole part 25is provided along the circumferential direction of the rotation axis C.In FIG. 10, a plurality of sets of the first bolt members 23 and thefirst hole parts 25 are provided, thereby improving the rigidity of thepassage forming member 22 and the impeller casing body 20 fixed to eachother.

The gear casing 16 accommodating the speed-increasing gear mechanism 2is disposed on the opposite side from the impeller 14A along the axialdirection with respect to the passage forming member 22. The gear casing16 includes a gear casing body 16 a, and a flange portion 16 b which isdisposed in the side of the passage forming member 22 with respect tothe gear casing body 16 a, and which faces the passage forming member 22so as to be perpendicular to the rotation axis C. The flange portion 16b is fixed to the passage forming member 22 by a second bolt member 29inserted along the axial direction.

The second bolt member 29 is inserted into a second hole part 30 formedfrom the flange portion 16 b (gear casing 16) over to the passageforming member 22, to fix the passage forming member 22 and the flangeportion 16 b (gear casing 16) to each other. At least one set of suchfixing structure including the second bolt member 29 and the second holepart 30 is provided along the circumferential direction of the rotationaxis C. In the example shown in FIG. 10, a plurality of sets of thefixing structure including the second bolt members 29 and the secondhole parts 30 are provided at equal intervals along the circumferentialdirection of the rotation axis C, to improve the rigidity.

The flange portion 16 b has a disk shape substantially perpendicular tothe rotation axis C, and includes an opening 31 having a substantiallycircular shape including the rotation axis C inside in the radialdirection. In the opening 31, a sealing member 27 is arranged so as torotatably support the rotor shaft 12 inside the impeller 14A in theaxial direction, and to seal the internal space S from the outside. Theflange portion 16 b may be configured to be dividable into a pluralityof pieces, whereby the sealing member 27 may be configured detachably.

The gear casing body 16 a has a bearing 26 on the wall surface definingthe outer casing of the turbo blower 18A. The bearing 26 rotatablysupports the rotor shaft 12 inside the sealing member 27 in the axialdirection. That is, the rotor shaft 12 is rotatably supported by thesealing member 27 of the flange portion 16 b and by the bearing 26 ofthe gear casing body 16 a, and the sealing member 27 and the bearing 26are arranged respectively coaxially with the rotation axis C.

When the centrifugal compressor 1 is assembled, the second bolt member29 shall be inserted into the second hole part 30 without any physicalinterference of the second bolt member 29 at the time of insertion. Asfor a gap M disposed along the rotation axis C between the flangeportion 16 b and the gear casing body 16 a, such insertion requires thegap M to be ensured longer than the length in the axial direction of thesecond bolt member 29. The gap M as described above is required to beensured by designing the rotor shaft 12 to be large in length due to theconvenience of the assembly. The rotor shaft 12 designed large in lengthdegrades the rotor build (in an example, a parameter in designingspecified by D/L² becomes smaller, when a diameter and a length in theaxial direction of the rotor shaft are denoted respectively by D and L).This may increase the risk of the shaft vibration occurring in the rotor4 and/or the contact of the impeller 14A with a peripheral member.Several aspects to be described below are capable of suitably copingwith the above.

It is noted that, in the aspects to be described below, theconfigurations corresponding to those in the reference art describedabove are denoted by the common reference signs, and the duplicatedescription will be appropriately omitted unless otherwise specified.

Embodiment

FIG. 2 is a cross-sectional configuration diagram of the vicinity of theturbo blower 18A according to one aspect of the present disclosure. FIG.3 is a cross-sectional view at an A-A line shown in FIG. 2. FIG. 4 is across-sectional view at a B-B line shown in FIG. 3.

The passage forming member 22 has, on the side thereof facing the gearcasing 16, a first protrusion 32 formed to protrude toward the gearcasing 16. The gear casing 16 has, on the side thereof facing thepassage forming member 22, a second protrusion 34 formed to protrudetoward the passage forming member 22. The first protrusion 32 isarranged inside the second protrusion 34 in the radial direction, andthe first protrusion 32 and the second protrusion 34 are arrangedrespectively coaxially with the rotation axis C. The first protrusion 32and the second protrusion 34 are configured so that the outside face inthe radial direction of the first protrusion 32 and the inside face inthe radial direction of the second protrusion 34 are contacted with eachother.

In the above-described arrangement where the first protrusion 32 isarranged inside the second protrusion 34 in the radial direction, thethermal expansion in the first protrusion 32 is greater than that in thesecond protrusion 34 when the turbo blower 18A is increased intemperature during the operation of the centrifugal compressor 1. As aresult, the gap between the first protrusion 32 and the secondprotrusion 34 is decreased, thereby providing good sealing property.

The first protrusion 32 and the second protrusion 34 in contact witheach other are fixed by a bolt member 36 inserted into a hole part 35formed along the radial direction. The configuration allows the boltmember 36 to be inserted from the outside in the radial direction at thetime of assembly. This eliminates the need for ensuring the gap Mallowing the second bolt member 29 to be inserted as in the referenceart described above by referring to FIG. 10. Accordingly, the rotorshaft 12 is enabled to be shortened in the axial direction (thecorresponding gap can be reduced compared to the gap M shown in FIG.10), thereby enabling to effectively suppress the risk of the shaftvibration occurring in the rotor 4 and/or the contact of the impeller14A with a peripheral member.

The hole part 35 into which the bolt member 36 is inserted at the timeof assembly is formed so as to be continuous from the second protrusion34 over to the first protrusion 32 when the first protrusion 32 and thesecond protrusion 34 are in a predetermined positional relation shown inFIG. 3. In the example shown in FIG. 3, the hole part 35 penetratesthrough the second protrusion 34 located outside, from the outside inthe radial direction toward the inside in the radial direction, and upto the inside of the first protrusion 32 located inside, from theoutside in the radial direction. In such positional relation, the boltmember 36 is inserted into the hole part 35, thereby enabling to fix therelative positional relation between the first protrusion 32 and thesecond protrusion 34. That is, the hole part 35 and the bolt member 36have the function of relative positioning of the first protrusion 32 andthe second protrusion 34.

At least one set of such components of the hole part 35 and the boltmember 36 is provided along the circumferential direction around therotation axis C. In the present embodiment, a plurality of sets of thehole parts 35 and the bolt members 36 are provided at equal intervalsalong the circumferential direction around the rotation axis C (when theupper direction in FIG. 3 is set as 0 degree, the sets of suchcomponents are respectively provided at the positions of 0 degree, 90degrees, 180 degrees, and 270 degrees).

FIG. 5 shows a modification of FIG. 3. In the present modification, thefirst protrusion 32 and the second protrusion 34 in contact with eachother include not only the fixing structure including the hole parts 35and the bolt members 36 described above, but also additional fixingstructure in which a pin member 38 is inserted into a pin hole part 37along the radial direction. This configuration enables further improvingthe rigidity at the time when the first protrusion 32 and the secondprotrusion 34 are fixed to each other (in other words, the rigidity ofthe first protrusion 32 and the second protrusion 34 fixed to each otherby the pin member 38 is improved in this way, thereby also enabling toprovide sufficient strength even with fewer sets of the hole parts 35and the bolt members 36 described above.

At least one set of the pin hole part 37 and the pin member 38 isprovided along the circumferential direction around the rotation axis C.In the present embodiment, a plurality of sets of the pin hole parts 37and the pin members 38 are provided at equal intervals along thecircumferential direction around the rotation axis C (when the upperdirection in FIG. 5 is set as 0 degree, the sets of the pin hole parts37 and the pin members 38 are respectively arranged at the positions of45 degrees, 135 degrees, 225 degrees, and 315 degrees).

FIG. 6 shows another modification of FIG. 3. FIG. 7 is a cross-sectionalview at a D-D line shown in FIG. 6. In the present modification, atleast one of the first protrusion 32 and the second protrusion 34 has areinforcing rib 40. In FIG. 7, the reinforcing rib 40 is formed alongthe radial direction over both a radially outer surface 34 a of thesecond protrusion 34 located outside the first protrusion 32 in theradial direction and a surface 34 b of the gear casing 16 where thesecond protrusion 34 is disposed. This configuration enables to furtherimprove the rigidity of the gear casing 16 where the second protrusion34 is disposed.

FIG. 8 shows another modification of FIG. 3. In the presentmodification, the first protrusion 32 of the passage forming member 22and the second protrusion 34 of the gear casing 16 are engaged with eachother via a spline 42. The structure of connecting the first protrusion32 and the second protrusion 34 enables to more effectively improve therigidity in the circumferential direction.

FIG. 9 shows another modification of FIG. 4. In the presentmodification, the first protrusion 32 and the second protrusion 34 areengaged with each other in an inlay structure 44. In the example shownin FIG. 9, the passage forming member 22 has, outside the firstprotrusion 32 in the radial direction, a concave portion 44 a allowing aconvex portion 44 b disposed at the tip of the second protrusion 34 tobe engaged with. The adoption of the inlay structure 44 described aboveenables to accurately position the first protrusion 32 and the secondprotrusion 34 along the radial direction. The accurate positioningenables to coaxially and accurately align the sealing member 27supported by the passage forming member 22 and the bearing 26 supportedby the gear casing 16, thereby enabling to more effectively prevent theshaft vibration from occurring in the rotor 4 and/or the impeller 14Afrom contacting with a peripheral member.

Moreover, a known component is available as needed, instead of acomponent in the embodiment described above within the scope notdeviating from the gist of the present disclosure. Some of thecomponents described above may be combined as needed.

The contents described in the above respective embodiments are grasped,for example, as follows.

(1) A centrifugal compressor (for example, the centrifugal compressor 1in the above described embodiments) according to one aspect of thepresent disclosure includes: a rotor shaft (for example, the rotor shaft12 in the above described embodiments) rotatably supported by a bearing(for example, the bearing 26 in the above described embodiments); animpeller (for example, the impeller 14A or 14B in the above describedembodiments) fixed to the rotor shaft in a tip side with respect to thebearing; a passage forming member (for example, the passage formingmember 22 in the above described embodiments) being arranged in a rearside of the impeller, and forming a passage communicating with a scrollpassage, together with a scroll member (for example, the impeller casingbody 20 in the above described embodiments) forming the scroll passageoutside the impeller in a radial direction; and a casing member (forexample, the gear casing 16 in the above described embodiments) disposedadjacent to an opposite side of the passage forming member from theimpeller along an axial direction. In the centrifugal compressor, thepassage forming member has a first protrusion (for example, the firstprotrusion 32 in the above described embodiments) formed to protrudetoward the casing member, the casing member has a second protrusion (forexample, the second protrusion 34 in the above described embodiments)formed to protrude toward the passage forming member, and the firstprotrusion and the second protrusion are fixed to each other by a boltmember (for example, the bolt member 36 in the above describedembodiments) inserted from an outside in the radial direction toward aninside in the radial direction.

According to the aspect of (1), the first protrusion of the passageforming member and the second protrusion of the casing member are fixedto each other by the bolt member. The bolt member is allowed to beinserted in the radial direction at the time of assembly, and thisconfiguration eliminates the need for ensuring the gap allowing the boltmember to be inserted, between the casing member and the passage formingmember. Accordingly, the rotor shaft is configured short in the axialdirection, thereby enabling to effectively suppress the risk of theshaft vibration occurring in the rotor and/or the contact of theimpeller with a peripheral member.

(2) In another aspect of the centrifugal compressor according to theaspect of (1), the first protrusion is arranged inside the secondprotrusion in the radial direction.

According to the aspect of (2), the first protrusion of the passageforming member and the second protrusion of the casing member under thestate where the first protrusion is arranged inside the secondprotrusion in the radial direction are fixed by the bolt member.Accordingly, the thermal expansion in the first protrusion is greaterthan that in the second protrusion when the passage forming member isincreased in temperature during the operation of the centrifugalcompressor. As a result, the gap between the first protrusion and thesecond protrusion is decreased, thereby providing good sealing property.

(3) In another aspect of the centrifugal compressor according to theaspect of (1) or (2), a plurality of the bolt members are arranged alonga circumferential direction of the rotor shaft.

According to the aspect of (3), the arrangement of the plurality of boltmembers along the circumferential direction of the rotor shaft enablesto effectively improve the rigidity of the fixing structure of the firstprotrusion and the second protrusion fixed by the bolt members.

(4) In another aspect of the centrifugal compressor according to any oneaspect of (1) to (3), the first protrusion and the second protrusion arefixed to each other by a pin member (for example, the pin member 38 inthe above described embodiment) inserted along the radial direction.

According to the aspect of (4), the pin member in addition to the boltmember fixes the first protrusion and the second protrusion, therebyproviding further higher rigidity. Such a configuration additionallyallowing the pin member to be inserted along the radial directioncontributes to shorten the length in the axial direction of the rotorshaft, and thus enables to effectively suppress the risk of the shaftvibration occurring in the rotor and/or the contact of the impeller witha peripheral member. In this case, since the pin member is able toimprove the rigidity of the first protrusion and the second protrusionfixed to each other, the number of the bolt members is able to bereduced.

(5) In another aspect of the centrifugal compressor according to any oneaspect of (1) to (4), a reinforcing rib (for example, the reinforcingrib 40 in the above described embodiment) is formed along the radialdirection, over both a radially outer surface of the second protrusionand a surface of the casing member.

According to the aspect of (5), the rigidity of the casing memberprovided with the second protrusion 34 is able to be improved further.

(6) In another aspect of the centrifugal compressor according to any oneaspect of (1) to (5), the first protrusion and the second protrusion areengaged with each other via a spline (for example, the spline 42 in theabove described embodiment).

According to the aspect of (6), the first protrusion and the secondprotrusion are engaged with each other via the spline, thereby enablingto provide higher rigidity, and further enabling to more effectivelyprevent the shaft vibration from occurring in the rotor and/or theimpeller from contacting with a peripheral member.

(7) In another aspect of the centrifugal compressor according to any oneaspect of (1) to (6), the first protrusion and the second protrusion areengaged with each other via an inlay structure (for example, the inlaystructure 44 in the above described embodiment).

According to the aspect of (7), the first protrusion and the secondprotrusion are engaged with each other via the inlay structure, therebyenabling to provide higher rigidity, and further enabling to moreeffectively prevent the shaft vibration from occurring in the rotorand/or the impeller from contacting with a peripheral member.

(8) In another aspect of the centrifugal compressor according to any oneaspect of (1) to (7), the passage forming member has a sealing member(for example, the sealing member 27 in the above described embodiments)configured to seal an internal space accommodating the impeller from anoutside, and to rotatably support the rotor shaft.

According to the aspect of (8), the passage forming member is providedwith the sealing member configured to seal the space accommodating theimpeller from the outside. The sealing member needs to be arrangedcoaxially and accurately with the rotor shaft so as to rotatably supportthe rotor shaft. The bolt member inserted along the radial directionfixes the casing member and the passage forming member with highrigidity as described above, thereby enabling to realize the coaxialarrangement of the sealing member with high accuracy.

(9) In another aspect of the centrifugal compressor according to theaspect of (8), the casing member has a bearing (for example, the bearing26 in the above described embodiments) configured to rotatably supportthe rotor shaft inside the sealing member in the axial direction.

According to the aspect of (9), the casing member is provided with thebearing configured to rotatably support the rotor shaft. The bearingneeds to be arranged coaxially and accurately with the rotor shaft so asto rotatably support the rotor shaft. The bolt member inserted along theradial direction fixes the casing member and the passage forming memberwith high rigidity as described above, thereby enabling to realize thecoaxial arrangement of the bearing with high accuracy.

(10) In another aspect of the centrifugal compressor according to anyone aspect of (1) to (9), the casing member accommodates aspeed-increasing gear mechanism (for example, the speed-increasing gearmechanism 2 in the above described embodiments) provided with the rotorshaft.

According to the aspect of (10), a geared compressor in which the casingmember accommodates the speed-increasing gear mechanism is capable ofsuppressing the vibration from occurring in the rotor shaft duringdriving, and further capable of preventing the impeller fixed to therotor shaft from contacting with a peripheral member.

1. A centrifugal compressor comprising: a rotor shaft rotatablysupported by a bearing; an impeller fixed to the rotor shaft in a tipside with respect to the bearing; a passage forming member arranged in arear side of the impeller, the passage forming member forming, togetherwith a scroll member forming a scroll passage outside the impeller in aradial direction, a passage communicating with the scroll passage; and acasing member disposed adjacent to an opposite side of the passageforming member to the impeller along an axial direction, wherein thepassage forming member has a first protrusion formed to protrude towardthe casing member, the casing member has a second protrusion formed toprotrude toward the passage forming member, and the first protrusion andthe second protrusion are fixed to each other by a bolt member insertedfrom an outside in the radial direction to an inside in the radialdirection.
 2. The centrifugal compressor according to claim 1, wherein aplurality of the bolt members are disposed along a circumferentialdirection of the rotor shaft.
 3. The centrifugal compressor according toclaim 1, wherein the first protrusion and the second protrusion arefixed to each other by a pin member inserted along the radial direction.4. The centrifugal compressor according to claim 1, wherein areinforcing rib is formed along the radial direction, over both aradially outer surface of the second protrusion and a surface of thecasing member.
 5. The centrifugal compressor according to claim 1,wherein the first protrusion and the second protrusion are engaged witheach other via a spline.
 6. The centrifugal compressor according toclaim 1, wherein the first protrusion and the second protrusion areengaged with each other via an inlay structure.
 7. The centrifugalcompressor according to claim 1, wherein the passage forming member hasa sealing member configured to seal an internal space accommodating theimpeller from an outside, and to rotatably support the rotor shaft. 8.The centrifugal compressor according to claim 7, wherein the casingmember has a bearing configured to rotatably support the rotor shaftinside the sealing member in the axial direction.
 9. The centrifugalcompressor according to claim 1, wherein the casing member accommodatesa speed-increasing gear mechanism provided with the rotor shaft.
 10. Acentrifugal compressor comprising: a rotor shaft rotatably supported bya bearing; an impeller fixed to the rotor shaft in a tip side withrespect to the bearing; a passage forming member arranged in a rear sideof the impeller, the passage forming member forming, together with ascroll member forming a scroll passage outside the impeller in a radialdirection, a passage communicating with the scroll passage; and a casingmember disposed adjacent to an opposite side of the passage formingmember to the impeller along an axial direction, wherein the passageforming member has a first protrusion formed to protrude toward thecasing member, the casing member has a second protrusion formed toprotrude toward the passage forming member, the first protrusion and thesecond protrusion are fixed to each other by a bolt member inserted froman outside in the radial direction to an inside in the radial direction,and the first protrusion is arranged inside the second protrusion in theradial direction.
 11. The centrifugal compressor according to claim 10,wherein a plurality of the bolt members are disposed along acircumferential direction of the rotor shaft.
 12. The centrifugalcompressor according to claim 10, wherein the first protrusion and thesecond protrusion are fixed to each other by a pin member inserted alongthe radial direction.
 13. The centrifugal compressor according to claim10, wherein a reinforcing rib is formed along the radial direction, overboth a radially outer surface of the second protrusion and a surface ofthe casing member.
 14. The centrifugal compressor according to claim 10,wherein the first protrusion and the second protrusion are engaged witheach other via a spline.
 15. The centrifugal compressor according toclaim 10, wherein the first protrusion and the second protrusion areengaged with each other via an inlay structure.
 16. The centrifugalcompressor according to claim 10, wherein the passage forming member hasa sealing member configured to seal an internal space accommodating theimpeller from an outside, and to rotatably support the rotor shaft. 17.The centrifugal compressor according to claim 16, wherein the casingmember has a bearing configured to rotatably support the rotor shaftinside the sealing member in the axial direction.
 18. The centrifugalcompressor according to claim 10, wherein the casing member accommodatesa speed-increasing gear mechanism provided with the rotor shaft.